Re: [PATCH] mm: check the return value of lookup_page_ext for all call sites

Andrew Morton
2016-05-27T20:02:48Z

On Thu, 26 May 2016 16:15:28 -0700 "Shi, Yang" <yang.shi@linaro.org> wrote:

> >>
> >> I hope we consider this direction, too.
> >
> > Yang, Could you think about this?
>
> Thanks a lot for the suggestion. Sorry for the late reply, I was busy on
> preparing patches. I do agree this is a direction we should look into,
> but I haven't got time to think about it deeper. I hope Joonsoo could
> chime in too since he is the original author for page extension.
>
> >
> > Even, your patch was broken, I think.
> > It doesn't work with !CONFIG_DEBUG_VM && !CONFIG_PAGE_POISONING because
> > lookup_page_ext doesn't return NULL in that case.
>
> Actually, I think the #ifdef should be removed if lookup_page_ext() is
> possible to return NULL. It sounds not make sense returning NULL only
> when DEBUG_VM is enabled. It should return NULL no matter what debug
> config is selected. If Joonsoo agrees with me I'm going to come up with
> a patch to fix it.
>

I've lost the plot here. What is the status of this patch?

Latest version:

From: Yang Shi <yang.shi@linaro.org>
Subject: mm: check the return value of lookup_page_ext for all call sites

Per the discussion with Joonsoo Kim [1], we need check the return value of
lookup_page_ext() for all call sites since it might return NULL in some
cases, although it is unlikely, i.e. memory hotplug.

Tested with ltp with "page_owner=0".

[1] http://lkml.kernel.org/r/20160519002809.GA10245@js1304-P5Q-DELUXE

[akpm@linux-foundation.org: fix build-breaking typos]
[arnd@arndb.de: fix build problems from lookup_page_ext]
Link: http://lkml.kernel.org/r/6285269.2CksypHdYp@wuerfel
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/1464023768-31025-1-git-send-email-yang.shi@linaro.org
Signed-off-by: Yang Shi <yang.shi@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

include/linux/page_idle.h | 43 ++++++++++++++++++++++++++++++------
mm/page_alloc.c | 6 +++++
mm/page_owner.c | 26 +++++++++++++++++++++
mm/page_poison.c | 8 +++++-
mm/vmstat.c | 2 +
5 files changed, 77 insertions(+), 8 deletions(-)

diff -puN include/linux/page_idle.h~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites include/linux/page_idle.h
--- a/include/linux/page_idle.h~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
+++ a/include/linux/page_idle.h
@@ -46,33 +46,62 @@ extern struct page_ext_operations page_i

static inline bool page_is_young(struct page *page)
{
- return test_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return false;
+
+ return test_bit(PAGE_EXT_YOUNG, &page_ext->flags);
}

static inline void set_page_young(struct page *page)
{
- set_bit(PAGE_EXT_YOUNG, &lookup_page_ext(page)->flags);
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return;
+
+ set_bit(PAGE_EXT_YOUNG, &page_ext->flags);
}

static inline bool test_and_clear_page_young(struct page *page)
{
- return test_and_clear_bit(PAGE_EXT_YOUNG,
- &lookup_page_ext(page)->flags);
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return false;
+
+ return test_and_clear_bit(PAGE_EXT_YOUNG, &page_ext->flags);
}

static inline bool page_is_idle(struct page *page)
{
- return test_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return false;
+
+ return test_bit(PAGE_EXT_IDLE, &page_ext->flags);
}

static inline void set_page_idle(struct page *page)
{
- set_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return;
+
+ set_bit(PAGE_EXT_IDLE, &page_ext->flags);
}

static inline void clear_page_idle(struct page *page)
{
- clear_bit(PAGE_EXT_IDLE, &lookup_page_ext(page)->flags);
+ struct page_ext *page_ext = lookup_page_ext(page);
+
+ if (unlikely(!page_ext))
+ return;
+
+ clear_bit(PAGE_EXT_IDLE, &page_ext->flags);
}
#endif /* CONFIG_64BIT */

diff -puN mm/page_alloc.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_alloc.c
--- a/mm/page_alloc.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
+++ a/mm/page_alloc.c
@@ -656,6 +656,9 @@ static inline void set_page_guard(struct
return;

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ return;
+
__set_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);

INIT_LIST_HEAD(&page->lru);
@@ -673,6 +676,9 @@ static inline void clear_page_guard(stru
return;

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ return;
+
__clear_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags);

set_page_private(page, 0);
diff -puN mm/page_owner.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_owner.c
--- a/mm/page_owner.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
+++ a/mm/page_owner.c
@@ -55,6 +55,8 @@ void __reset_page_owner(struct page *pag

for (i = 0; i < (1 << order); i++) {
page_ext = lookup_page_ext(page + i);
+ if (unlikely(!page_ext))
+ continue;
__clear_bit(PAGE_EXT_OWNER, &page_ext->flags);
}
}
@@ -62,6 +64,7 @@ void __reset_page_owner(struct page *pag
void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
{
struct page_ext *page_ext = lookup_page_ext(page);
+
struct stack_trace trace = {
.nr_entries = 0,
.max_entries = ARRAY_SIZE(page_ext->trace_entries),
@@ -69,6 +72,9 @@ void __set_page_owner(struct page *page,
.skip = 3,
};

+ if (unlikely(!page_ext))
+ return;
+
save_stack_trace(&trace);

page_ext->order = order;
@@ -82,6 +88,8 @@ void __set_page_owner(struct page *page,
void __set_page_owner_migrate_reason(struct page *page, int reason)
{
struct page_ext *page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ return;

page_ext->last_migrate_reason = reason;
}
@@ -89,6 +97,12 @@ void __set_page_owner_migrate_reason(str
gfp_t __get_page_owner_gfp(struct page *page)
{
struct page_ext *page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ /*
+ * The caller just returns 0 if no valid gfp
+ * So return 0 here too.
+ */
+ return 0;

return page_ext->gfp_mask;
}
@@ -99,6 +113,9 @@ void __copy_page_owner(struct page *oldp
struct page_ext *new_ext = lookup_page_ext(newpage);
int i;

+ if (unlikely(!old_ext || !new_ext))
+ return;
+
new_ext->order = old_ext->order;
new_ext->gfp_mask = old_ext->gfp_mask;
new_ext->nr_entries = old_ext->nr_entries;
@@ -193,6 +210,11 @@ void __dump_page_owner(struct page *page
gfp_t gfp_mask = page_ext->gfp_mask;
int mt = gfpflags_to_migratetype(gfp_mask);

+ if (unlikely(!page_ext)) {
+ pr_alert("There is not page extension available.\n");
+ return;
+ }
+
if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
pr_alert("page_owner info is not active (free page?)\n");
return;
@@ -251,6 +273,8 @@ read_page_owner(struct file *file, char
}

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ continue;

/*
* Some pages could be missed by concurrent allocation or free,
@@ -317,6 +341,8 @@ static void init_pages_in_zone(pg_data_t
continue;

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ continue;

/* Maybe overraping zone */
if (test_bit(PAGE_EXT_OWNER, &page_ext->flags))
diff -puN mm/page_poison.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/page_poison.c
--- a/mm/page_poison.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
+++ a/mm/page_poison.c
@@ -54,6 +54,9 @@ static inline void set_page_poison(struc
struct page_ext *page_ext;

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ return;
+
__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
}

@@ -62,6 +65,9 @@ static inline void clear_page_poison(str
struct page_ext *page_ext;

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ return;
+
__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
}

@@ -70,7 +76,7 @@ bool page_is_poisoned(struct page *page)
struct page_ext *page_ext;

page_ext = lookup_page_ext(page);
- if (!page_ext)
+ if (unlikely(!page_ext))
return false;

return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
diff -puN mm/vmstat.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites mm/vmstat.c
--- a/mm/vmstat.c~mm-check-the-return-value-of-lookup_page_ext-for-all-call-sites
+++ a/mm/vmstat.c
@@ -1061,6 +1061,8 @@ static void pagetypeinfo_showmixedcount_
continue;

page_ext = lookup_page_ext(page);
+ if (unlikely(!page_ext))
+ continue;

if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
continue;
_